A doctoral candidate from Boston. A livestock veterinarian from Minnesota. A teacher from Pennsylvania. All have converged on the historic hamlet of Harpers Ferry, West Virginia, on this soft May morning for a single reason: because the Magician lives here, and the Magician has said that the signs are good.
The Magician is famous among the cognoscenti for his ability to make the Glowworm appear. Go to the Magician, it is said, and you cannot fail to encounter it. What’s more, the worm will do you no harm. Its bite always misses in the presence of the Magician.
Everyone wants to see the Glowworm in its glory, but no one wants to get bitten by it.
The Glowworm, Crotalus horridus, is the timber rattlesnake, the Moby Dick of eastern reptiles. The Magician is W. H. Martin, a former southern dirt farmer turned naturalist who is widely recognized as one of the most knowledgeable and accomplished snake hunters in the Appalachians. Just as Darwin cultivated stockmen and pigeon breeders for their familiarity with the mysterious laws of inheritance, biologists interested in rattlesnakes have beaten a path to Martin’s door. Much of what he knows isn’t available in libraries.
Snake finding is Martin’s passion. He has refined it into a modern, analytic obsession with mapping and counting, the spadework of population biology. currently he is working on a two-year rattler census for the Maryland Department of Natural Resources. One reason his work is of interest to zoologists and state conservation offices is its novelty. Unlike bald eagles or grizzly bears, snakes are maddeningly difficult to count, and hence the baseline data from which population trends can be abstracted are hard to come by. In general, snakes do not mark territories, leave distinctive signs, or even show themselves aboveground with any frequency, so a patch of woods where snakes are abundant may be practically indistinguishable from one where they are absent.
There are no rattlesnakes in Martin’s house, nor in the blossoming orchards and croplands surrounding it. Yet he lives at the heart of the snake’s domain, since his farmstead lies near the Blue Ridge of Virginia. This lofty ripple of forested rock, raised when Africa plowed into North America over 300 million years ago, is the eastern bulwark of a thousand-mile chain of ancient mountains stretching from Atlanta to Quebec. A scale model of the ridge, pieced together from dozens of raised-relief maps published by the U.S. Geological Survey, sprawls across the longest wall in Martin’s house. Many of the maps are peppered with inked-in red dots indicating sites where the snake is active. Martin, at 51, has spent much of his life assembling these swarms of red dots.
Over a leisurely breakfast in his kitchen, Martin announces that the day’s predicted warmth augurs well for producing timber rattlers. His guests, all members of the tight fraternity of Glowworm enthusiasts, are eager to get up to the ridgetops, and they fidget a bit as the morning advances. Cats look in at doorways. Bobwhites whistle in the dewy grass behind the barn. No point getting there before ten, Martin says. They won’t come out before then.
Like Martin’s guests, the timber rattler needs warmth. Unlike them, however, it cannot generate its glow metabolically or regulate it hormonally and hence must exploit sources in its environment. Despite its nickname--borrowed from the familiar nocturnal, luminescent insect of summer--the Glowworm can glow only in the heat of the day.
Frost will paralyze and eventually kill any rattlesnake, no matter how many calories are available to it. In the fall, just before freezing temperatures become commonplace in the Blue Ridge, the timber rattler retreats downward into deep fractures in exposed rock, where it finds frost-free crevices that will shelter it all winter. This period of dormancy, or hibernation, can last as long as eight months, during which the snake remains virtually motionless and its body temperature slowly drops along with that of the surrounding rock, bottoming out in late February at temperatures as low as 40 degrees. When, in the spring, the temperature curve inverts, the snake migrates back toward the thawed surface. For a brief interval around May 1, its need to warm its chilled body overcomes its normal discretion, and the snake suns itself in the open. This phenomenon is known as emergence. At every latitude and altitude within the timber rattler’s range there are perhaps three or four spring days when basking conditions become optimal. Unbelievers argue that it is his knowledge of these conditions rather than any freakish or uncanny wizardry that permits the Magician to make rattlers appear as if on command.
This is an increasingly rare skill. The timber rattlesnake, once widespread throughout the East, is now extinct in two states and endangered in eight others. Two tendencies make the timber rattler particularly vulnerable. The snake concentrates in numbers at wintering sites, or dens, thus becoming potentially easy prey. And when it emerges, it must bask in the warmth of the sun on exposed ledges. Other snakes also winter in dens, and other snakes also bask in the open, but no other temperate-zone snake grows as big, matures as late, or reproduces as slowly as the timber rattler.
A biologist would say that the timber rattlesnake has adopted a reproductive strategy typical of sizable long-lived animals that when fully grown have few natural enemies. Low adult mortality enables such animals to sustain their numbers without producing a large annual influx of young. Mice and mosquitoes pursue an opposite approach, counteracting high losses in all age classes by breeding early and often.
Until recently even experienced snake hunters thought the timber rattler was a frequent breeder, in the manner of garter or water snakes, since most of the rattlers they found were pregnant females, identifiable by their heavy and distended abdomens. What the hunters didn’t know was that pregnant females are particularly easy to find, thanks to their habit of staying near rocky and exposed basking sites. These hunters never saw the nonpregnant females, which don’t seek out the sun after the brief period of emergence but spend the summer in deep woods as much as two miles from their den crevices. The timber rattler population is spread thin-- perhaps one snake on average in every 60 acres--and so the snakes are nearly impossible to find.
The foremost academic student of the timber rattler, William S. Brown of Skidmore College, has documented the snake’s extended breeding cycle by capturing adult females, noting their condition, marking them, releasing them, and capturing them again at later dates. Not one of his recaptured females was pregnant in successive years, or even in alternate years, and he concluded that female rattlers in the north typically require three or more active seasons to produce a litter of from 6 to 12 young. One summer is needed to build up body mass, much of it in the form of chunky strings of yellow fat laid down along the base of the abdominal cavity; another to increase weight further and swell the paired ovaries with yolky acorn-size eggs; and a third, largely spent basking, to produce live young from the eggs, with the help of sperm stored from mating late the previous summer. Brown’s data suggest, in fact, that four and even five years are not uncommon intervals between births in his study area, the Adirondack foothills. Four or five years is a long time for a mature female of any vertebrate species to devote to a single birth event.
The actual period of pregnancy has never been observed to last more than a single summer. and it is apparently the earlier, weight-gaining portion of the cycle that is extended to two or more summers in cool climates. Timber rattlers from Alabama, for example, may be able to complete this essential bulking-up phase in a single March-to-November season, while those from Brown’s New York populations, which are active only from May to September, typically require longer. At any rate, the three-, four-, and five-year cycles he documented put his female rattlers far ahead of human mothers and right up with whales and elephants as all- time poky breeders.
It was Martin who tipped Brown to the existence of an extended cycle. He had done some mark-recapture work of his own that indicated reproductive intervals of two to four years, and consequently he had become skeptical of the shorter periods proposed, with scant evidence, in the literature. He noted that rattlesnakes originally evolved in the hot, dry climate of the southern United States and northern Mexico. In Martin’s opinion the snake’s habits reflect the strain of having spread into the harsher, colder clime of the Appalachians. As an example of this harshness he cites the summers of 1989 and 1992, which were unusually wet and cool in the Blue Ridge and which perhaps prevented high-altitude female rattlers from achieving, through sunbathing, the internal temperatures required for timely gestation. They were the only years in his experience in which he observed near-term females reentering their dens in the fall without having given birth. He never saw any of the ’89 mountaintop females or their young again (the fate of the 1992 females won’t be known for another month or so), and he believes that above certain elevations an entire year’s crop of newborns may have been wiped out.
According to Martin, the timber rattler’s current scarcity in good habitat is by no means purely a product of a long backcountry tradition of snake hunting. Look instead, he argues, for the varying effects snake bagging has had across a range of climatic and topographic conditions, especially as those conditions relate to denning and basking behavior.
About 8,000 years ago, following the northernmost retreat of the glaciers, the Appalachians became somewhat warmer than they are today; they remained so for several thousand years. Martin suggests that it was during this warm spell that the timber rattler expanded its range north to Maine and southern Quebec, where it was still present in historical times. Here, he believes, the animal reached the limits of its thermal tolerance. In his published work Martin has shown how the snake’s sensitivity to cold is reflected in the maximum elevation of den sites: in southern Virginia, at the heart of the snake’s range, dens may be as much as 4,500 feet above sea level; but at the range’s northern extreme in New York State, they top out at 1,300 feet.
The cooling that followed reduced these northern-fringe rattlers to a scattering of relict populations at the most favorable sites, where deeply fissured south-facing ledges overlooked warm, low-lying valleys, the same valleys that snake-killing farmers would later invade in droves. The scarcity and isolation of these scattered colonies made them peculiarly susceptible to piecemeal extermination, since they could not be repopulated from nearby groups. This combination of limited habitat and human pressure, Martin argues, has resulted in the timber rattler’s disappearance from nearly all of northern New York and New England in recent times. An analogous process is under way in northeastern Georgia and western North Carolina, where the mountains were never scraped bare by moving ice, and large areas of otherwise prime habitat provide very few treeless exposures where pregnant females can bask. in the densely wooded Appalachians the connection between rattlers and exposed rock is so intimate that likely sites can be identified from satellite photos. One of the best and most remote dens Martin has found in recent years--home to over 200 snakes--he first glimpsed, serendipitously, from the window of a commercial jetliner.
Breakfast is over, and after an hour on the interstate the Magician’s party turns toward the forested wall of the Blue Ridge. A steep, serpentine road carries them out of the balmy, fully leafed valleys to the windy chill of the ridgetops, where the oaks are still naked and great gulfs of air fall away from the roadsides. There are dens lower down, Martin says, but they’re already empty for the summer, the hungry snakes dispersed into the woods. Up here, they’re just coming out. He has calculated that the zone of peak emergence moves upslope at about 120 vertical feet per day, correlating closely with the blossoming of the redbud and the unfurling of the first oak leaves.
His party parks at a trailhead. They will walk three miles to the den. The Magician has said that it is one of his best, sheltering well over 100 rattlers. Once upon a time there were thousands of dens like this in the eastern mountains, but nearly all have suffered from human depredations, and some stand empty. Only undisturbed dens concentrate so many snakes. As far as Martin knows, he is the only person who can locate this one.
Martin waits at the edge of the clearing while his guests shoulder their gear. A small, wiry, and sunburned man, he would look right at home in a nineteenth-century daguerreotype, thanks to his lush gray curls and his patriarch’s beard. His guests already know, however, that his air of antique dignity is somewhat misleading, for although he is utterly serious about rattlers, he is nevertheless a coyote for laughs and, if so moved, will hoot and cackle with the best.
All of the party are wearing ankle boots. None has ever been treated for snakebite, but they appear a bit thoughtful nonetheless. They needn’t worry for the moment, however, since the just-greening woods are 99 percent rattler-free at this time of the year, all the snakes within miles having concentrated in just a few widely scattered rocky places, mostly on sunny south-facing slopes, where they assembled seven months earlier to move underground.
Like Dracula, every timber rattler has a fixed subterranean address, its den site, where it submits to being chilled annually throughout its quarter-century life span. In a series of experiments using Y-shaped corridors, Brown showed that newborn rattlers can and will consistently retrace forks taken earlier by adults, apparently by detecting olfactory cues picked up by their flickering tongues, their main sensing organ for smell. This, he believes, may be the primary means by which newborns become associated with ancestral dens (snakes are not born inside dens but at summer basking sites, which may be as much as a quarter-mile away). At any rate, one practical way to assess timber rattler populations, as Martin has been doing every spring for 30 years, is to locate den sites and count snakes during emergence. Then, as the summer progresses, he will also count the number of gestating females, who usually stay close to the ancestral den. Martin knows what a healthy den looks like and what sorts of habitat might be expected to support one. With so few healthy dens left, this is privileged information.
The air is not warm but the Magician’s party is, having dogged him several miles along a rugged dirt trail occasionally greased with bear turds. Martin, who is as light, quick, and impish as a lizard, is also not weighed down under many pounds of photo equipment. He stops and points up through the just-leafing treetops at a 2,600-foot crag looming overhead. After we check the first den, he says, we’ll hit another near the top of that thing. His guests, their faces blotched from exertion, stare upward in dismay.
At last he turns off the trail and starts up a wooded slope. Before long a splash of light up ahead opens into an enormous sun-filled and uptilted bowl brimming with humpbacked gray boulders, some as large as small elephants. Martin stops and nods at the rim of woods high above. That, he says, is the den site.
The party leaves the shade and continues climbing. After 20 minutes they reassemble near the top, where the rockslide peters out in a tangle of last year’s grapevines. Look sharp, Martin cautions. Here they are.
The rattlers, which are sunning, remain motionless and are hard to pick out among the vines and leaf litter. Once noticed, however, they seem to pop out in bunches. They lie full length in the low places, like drowned worms after a cloudburst.
Of course, there is some low-toned discussion of the size of the reptiles in view, a couple of which appear large enough in a visitor’s mind to swallow footballs. The estimates of actual size necessarily remain speculative, since attempts to apply tape measures to big rattlesnakes are foolish without special equipment, such as a stout tube of clear plastic, or a foam-lined squeeze box. Martin, who has investigated the question in detail, believes that there may be a few timber rattlers remaining in the Appalachians that exceed five feet and five pounds, though he has not met one. They would probably be male, since females grow less rapidly after the age of reproduction and are smaller on average. Martin doesn’t entirely discount reports of six-footers, dating from the early years of this century, although he wishes that the chief compiler of these reports-- Raymond Ditmars of the Bronx Zoo--had been a more conscientious observer and had left better evidence.
Timber rattlers, although big, are not the biggest rattlers. That honor indisputably belongs to the eastern diamondbacks (Crotalus adamanteus) of the Southeast’s coastal pinewoods, record males of which may top seven feet in length and weigh over 15 pounds, ranking them among the most massive venomous beasts on earth. In recent years Martin has begun traveling again on his own to the Georgia and Florida lowlands in search of these snakes, but he has found them to be much less abundant than in the 1960s, when he previously searched for them.
After a minute the veterinarian quickly sets up his camera and tripod. He wants one snake in particular, a big coal black male watching him from a yard away. According to Martin, black rattlers are rare except in heavily wooded dens at high altitudes and elevations, where their coloring presumably affords them better heat gain from sunlight. Even so, only a single all-black population has been confirmed (at a den in northern New York). Martin attributes this to a sort of balancing selection: in cool or wet years the black form has a thermal advantage, but its greater conspicuousness makes it more vulnerable to predation, and hence it never becomes dominant at lower elevations.
Martin consents to pose the big black for the camera and snatches it up by the tail. The snake doesn’t like this at all, and it begins to lash back and forth wildly, snapping at Martin’s shins and spraying a repellent musk from its vent. The commotion excites other snakes nearby, and they set up a furious buzzing. Martin, with appalling nonchalance, pushes the black’s venom-filled head away from his leg with the hooked end of his snake stick. When the reptile is panting visibly, too winded to bolt away, he lowers it into a neat coil for the camera, then flips open his notepad and begins writing.
Meanwhile the black’s alarmed den-mates have backed into rock crevices and out of sight. A couple of them are still buzzing. This sound has often been described, but without much success. It is visible as a hummingbird-wing blur where the tip of the snake’s tail should be, as the rattle whips back and forth.
Unlike a child’s toy, the rattle has nothing inside it but is a string of hollow, tough, and dry segments comparable to a stack of straw hats. Each of the hats is pinched at its base, securing it loosely to the crown of the next, and each hat once formed the base of the stack, where it was firmly attached to the snake. Every time the snake sheds its skin the lowest hat comes loose, pushed up by a fresh one from below. The highest and oldest hats tend to wear out and break off easily, and consequently snakes are rarely found in possession of more than a dozen or so, though they can produce more than twice as many in a lifetime.
The buzz itself is the sound of the hats clacking dryly and unmusically against their neighbors. Since about 700 or more contacts occur per second--far too many for the human ear to distinguish--the buzz has a sizzling or sibilant quality. Most students agree that the rattle probably evolved as a warning device, helping these slow-moving vipers to persuade would-be tramplers or predators to keep well away, or else. There is something about the sound that makes one’s neck hairs stand up, something absent from a cricket’s chirp or a cicada’s rasp.
All told there are about 30 species of rattlesnake. Some of the larger species will occasionally begin buzzing, even if concealed in good cover, when a two-legged intruder is ten yards away. But the Glowworm, as is typical of snakes from heavily forested ecotypes, will often remain quiet and motionless until approached within inches and hence cannot be hunted by ear.
Over a five-year period Martin marked 70 different snakes, predominantly females, at this den by painting numbers on their rattles. It is his opinion that undisturbed dens typically shelter twice as many adult females as males, despite a nearly even ratio among newborns. Males wander farther, and perhaps they suffer increased mortality as a result. But the surest sign that a den is being decimated by snake hunters is a reversal of this imbalance, since hunters can usually find and take only pregnant females. The last den in Rhode Island, which vanished in 1970, contained nothing but males during its final decade.
The Magician’s guests now have no doubts about the communal and patchy character of timber rattler populations. Each den, in fact, is a sort of predatory superorganism, not unlike a bat cave, in that its component individuals, although anchored to a specific base, periodically disperse across a much larger foraging area. Martin estimates this potential foraging zone as a circle six miles in diameter centered on the den entrance, since he rarely finds marked snakes at greater distances. New dens are presumably founded when wandering individuals enter unoccupied wintering crevices and other snakes follow. Some such process must have allowed the timber rattler to expand its range north from the southernmost Appalachians to the Canadian border following the last glacial retreat. Today, however, there is very little evidence that timber rattlers are recolonizing dens from which they have been extirpated, even in undeveloped areas.
In the most ambitious survey of its kind ever attempted, Martin and several colleagues recently compiled field estimates of rattler populations at 312 remaining den sites in Pennsylvania. They estimated that fewer than one-quarter of the sites sheltered eight or more adult females, the minimum number that Martin speculates is necessary to sustain long-term viability. And so the survey became a prediction: 75 percent of the Pennsylvania dens may not, under current conditions, be expected to survive. The authors attributed this decline to the inability of most den colonies to withstand repeated losses of pregnant females to snake hunters. The state of Pennsylvania, which sponsored the survey, now treats the timber rattler as a game animal and allows limited hunting. This approach is no longer an option in New York, New Jersey, and the New England states, where the species, when not extinct, is firmly established on endangered- species lists. Martin would like to see hunting end throughout the Appalachians so that the collapse in the Northeast will not be repeated elsewhere.
Appalachian rattler dens have a long history of human visitation. In colonial times they produced thousands of carcasses that were boiled down to extract a widely used liniment known as snake oil. More recently the popular animus against their denizens supported a breed of backwoods vigilantes who received payment in cash for every rattle turned in to the authorities. Today bounty payments are all but gone, but markets still exist for rattlesnake skin and for live animals for collectors.
The Magician will tell you all this if you ask him, but it is not the reason he and his guests are high up in a wooded cove of the Blue Ridge this morning. They are here to see snakes, in the kind of numbers visible only at remote dens during the narrow window of emergence. Before long they will climb down from this site and trek to another. They, like more and more visitors to snake dens these days, are coming to see what is there rather than to subtract what can be carried away. The Glowworm has responded by revealing aspects of itself not imagined before. This is no sleight of hand but a welcome access of light.